This application claims priority on Japanese Patent Application No. 2000-59458 filed on Mar. 3, 2000, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to clutch mechanisms. More particularly, the present invention relates to a clutch mechanism for use in a dual-mode rotary tool having a screw-driving mode and a drill mode that can control the upper limit of the output torque of an epicyclic reduction gear mechanism by adjusting the force that holds an internal gear of the epicyclic reduction gear mechanism.
2. Description of the Related Art
A typical dual-mode rotary tool having a screw-driving mode and a drill mode (referred to as a screwdriver/drill hereinafter) is provided with a clutch mechanism which can control the upper limit of the output torque of the tool. FIG. 3A shows one example of such a clutch mechanisms having a rotatable internal ring gear 30 as part of an epicyclic reduction gear mechanism that transmits torque from a motor to a spindle. The internal ring gear 30 has on an end surface thereof a plurality of axial cam protrusions 31 with each protrusion including a pair of circumferentially inclined guide slope surfaces 32. As shown in FIG. 3B, the clutch mechanism further includes press means, such as balls 33, pressed against the notched end surface of the internal ring gear 30 via a flat washer 34 by a biasing means such as a coil spring (not shown). In this way, the press means prevents the internal gear 30 from rotation by holding the balls 33 against the cam protrusions 31.
In accordance with this clutch mechanism, if a load exceeding the biasing force of the coil spring is applied to the internal gear 30, the balls 33 ride up the guide slope surfaces 32 over the cam protrusions 31, allowing idle rotation of the internal gear 30 and thus interrupting the transmission of the motor torque to the spindle of the rotary tool.
In addition to the clutch mode, the above-described clutch mechanism also provides a drill mode in which the clutch remains engaged and is prevented from slipping. More particularly, in this mode, a lock member or a stopper is directly pressed against and locks up the flat washer 34 so as not to allow rotation of the internal gear 30, thus maintaining the rotation of the spindle regardless of the load applied to the spindle. As shown in FIG. 3C, when a load is applied to the too in this mode, the clearance between components may cause the balls 33 to be lifted off the guide slope surfaces 32 without riding over the cam protrusions 31.
While the foregoing clutch mechanism achieves its intended objective, it suffers from a number of deficiencies that reduce its utility. For example, in this arrangement, P, the point of contact of the lower ball 33 with the guide slope surface 32, remains at the top corner of the cam protrusion 31, regardless of whether the rotary tool is in the operating condition shown in or in FIG. 3C. This means when the balls 33 are lifted, the apparent angle of the cam decreases (angle xcex1 (FIG. 3B) greater than angle xcex2 (FIG. 3C)), thus increasing the force acting in the axial direction on the balls 33 or the force that pushes up the ball 33 and the flat washer 34. This in turn increases the possibility of the ball 33 accidentally riding over the cam protrusion a 31, thereby disengaging the clutch. It should be noted that the same may occur if the balls are replaced with pins having a spherical bottom end. In addition, the increased force acting in the axial direction tends to cause more wear and/or damage to tool components, such as the flat washer or any other type of a stopper subjected to or bearing the axial force.
In view of the above-identified problems, an important object of the present invention is to provide a clutch mechanism for use in a dual-mode rotary tool having screw-driving and drill modes that is capable of reliably preventing unintended disengagement of the clutch in the drill mode so as to minimize wear or damage to components of the tool.
The above object and other related objects are realized by the invention, which provides a clutch mechanism for use in a rotary tool having screw-driving and drill modes. The clutch mechanism comprises: an epicyclic reduction gear mechanism including an internal gear rotatably held within a housing; a plurality of axial cam protrusions provided on an axial end surface of the internal gear, with each cam protrusion having at least one guide slope surface; a plurality of axially movable press members; biasing means for pressing the press members against the axial end, surface of the internal gear so as to secure the cam protrusions by causing the press members to interfere with the guide slope surfaces of the cam protrusions; and means for selectively regulating the axial movement of the press members away from the axial end surface. In this clutch mechanism, each press member comprises an axial body which is disposed orthogonally to the axial end surface of the internal gear and which includes at least one slope surface, with the slope surface being slidable on the guide slope surfaces due to revolution of the cam protrusions so as to move the axial body away from the axial end surface of the internal gear. According to this mechanism, although the axial bodies (i.e., the press members) may be lifted along the cam protrusions in the drill mode, they do not ride over the cam protrusions, thus preventing unintended clutch disengagement or slippage. Moreover, as the axial force acting on the axial bodies remains relatively small, the impact on tool elements such as the regulating means does not become excessive, thus protecting these elements from excessive wear and damage.
According to one aspect of the present invention, the slope surface of each axial body has the same inclination as the at least one guide slope surface of each cam protrusion. This arrangement stabilizes the operation of the axial bodies in conjunction with the cam protrusions, enhancing the performance the clutch mechanism regardless of whether the rotary tool is in the drill mode or the screwdriver mode.
According to another aspect of the present invention, each axial body is adapted to slide along the guide slope surfaces in parallel to itself relative to the internal gear.
According to still another aspect of the present invention, the axial bodies are arranged in a circumference and the cam protrusions are also arranged in a circumference so as to correspond in number and position with the axial bodies.
According to yet another aspect of the present invention, each axial body has first and second axial ends, with the first end opposing the means for biasing and the second end abutting the axial end surface of the internal gear. Additionally, the slope surface of each axial body is a circumferentially chamfered edge provided on the second end thereof.
According to one feature of the present invention, each cam protrusion includes two circumferential guide slope surfaces symmetrical about an axis of the protrusion such that the axial bodies are movable away from the cam protrusions parallel to themselves while maintaining surface-to-surface contact between the guide slope surfaces and the chamfered edges.
According to another feature of the present invention, the means for biasing is a coil spring fitted between the means for regulating and the axial bodies. The means for regulating is a sleeve member adapted to be screw-fed through an external operation to change its axial position, and thus the biasing force, of the coil spring acting on the internal gear via the axial bodies.
According to still another feature of the present invention, the clutch mechanism may further comprise a washer disposed between one end of the coil spring and the axial bodies, and the sleeve member has an end distal to the axial bodies and the washer and an end proximal to the axial bodies and the washer. The distal end forms a radially extending flange thereat for abutting another end of the coil spring, and the proximal end can be brought into abutment against the washer through an external operation of the sleeve member so as to securely hold the cam protrusions against revolution via the axial bodies, regardless of a load imposed on the rotary tool.
According to yet another feature of the present invention, each axial body and each cam protrusion have an apparent cam angle and are adapted to maintain the apparent cam angle regardless of the operating condition of the rotary tool.
According to one practice of the present invention, each axial body is a cylindrical pin slidably held through a gear case of the rotary tool.
Other general and more specific objects of the invention will in part be obvious and will in part be evident from the drawings and descriptions which follow.